Testing probe construction

ABSTRACT

Precise testing of printed circuit boards having closely spaced contact bores is made possible by an apparatus comprising a plurality of predisposed, closely spaced contact needle probes each of which has a flexible, slender construction to automatically compensate for spacing variations of the contacts within manufacturing tolerances and each of which may have a detachable contact head to compensate for variations in contact bore diameters. A generally spherical contact probe head surface assures a uniform contact with the edge of the bore and hence equal contact resistances, regardless of the angle of the probe with the bore.

United States Patent [151 3,676,776 Bauer et al. 1 July 11, 1972 [54]TESTING PROBE CONSTRUCTION OTHER PUBLICATIONS [72] Inventors: FranzBauer, Pullach; Karl Friedrich Besemer, Planegs; Goflhard Kinner, Mu-

nich, all of Germany Siemens Aktiengesellschaft, Berlin and Munich,Germany Jan. 19, 1970 Assignee:

Filed:

App]. No.:

[5 6] References Cited UNITED STATES PATENTS 3,274,534 9/1966 Shortridge..324/l58P 3,512,084 5/1970 Roberts ..324/72.5

19b 12b llb III J. F. McDonald Logic Function Indicator Probe IBMTechnical Disclosure Bulletin 8(4) 9/65 pp. 661, 662

J. F. Hallenback Electrical Contacting Probe IBM Technical DisclosureBulletin 9(5) 1966 p. 453

Primary Examiner-Michael J. Lynch Attorney-Hill, Sherman, Meroni, Gross& Simpson [57] ABSTRACT Precise testing of printed circuit boards havingclosely spaced contact bores is made possible by an apparatus comprisinga plurality of predisposed, closely spaced contact needle probes each ofwhich has a flexible, slender construction to automatically compensatefor spacing variations of the contacts within manufacturing tolerancesand each of which may have a detachable contact head to compensate forvariations in contact bore diameters. A generally spherical contactprobe head surface assures a uniform contact with the edge of the boreand hence equal contact resistances, regardless of the angle of theprobe with the bore.

10 Claims, 7 Drawing Figures lie 17 PATENTEDJUL 1 1 m2 SHEET 3 BF 3Fig.4

VENTORS F 2 Bauer" ar/ Besagmer 5017/60 42 417 er BY ATTYS.

TESTING PROBE CONSTRUCTION BACKGROUND OF THE INVENTION 1. Field of theInvention This invention generally relates to an automatic electricalcontact testing apparatus for the simultaneous electrical connection ofa large number of contacts spaced a small distance from one another.More particularly, the invention contemplates an apparatus for thetesting of metallized bore-type contacts of a printed circuit card orcircuit plaque wherein the contacts to be tested are closely spaced andthe electrical test equipment has a number of contact needle probescorresponding exactly in number and generally in position to thecontacts which are tested by simultaneous pressing of all of the testingprobes on all of the contacts to be tested.

2. Prior Art For the electrical testing of printed circuit cards bymeans of automatic testing devices, a large number of the contactsdisposed on the circuit card must be connected simultaneously with theautomatic testing devices. In these cases the uniformity of the contactresistances must be precise because a comparatively high specificcurrent load must be accommodated in the case of many of the varioustesting procedures. Also, the bearing forces of the contacts may notexceed or be less than predetermined tolerances.

In the German Gebrauchsmuster Patent 1,950,659, there is disclosed atesting apparatus for printed circuit cards wherein the connection withthe contacts of the circuit card are established by means of brassplates which are provided with inserted pointed contact needles. Thisprior art contact testing device, however, does not permit theachievement of sufficiently uniform contact resistances. One reason forthis nonuniformity resides in the fact that the metallized bore typecontacts of the circuit card may not always be disposed at the mostaccurate grid distances due for example, to variations withinmanufacturing tolerances. Where these variations occur, the pointedtesting contact needles which must be accurately seated in the bores arepushed or moved out of their original positions when they assume thetesting position so that the various pointed contact needles aredeflected to various directions and by various amounts. Because theseprior art needles sit differently on the contacts of the circuit cardbeing tested a different contact resistance results.

SUMMARY OF THE INVENTION The above noted problems and disadvantages ofthe prior art are overcome by the present invention disclosed hereinwhich provides a contact testing apparatus wherein despite thevariations within the manufacturing tolerances in the contact grid fieldof the circuit board, the bearing surfaces between the test probes andthe individual bore-type contacts are substantially the same andsubstantially the same low contact resistances are found on allcontacts.

This result is accomplished in the instant invention by providing acontact testing apparatus wherein the ends of the contact needle probesbeing pressed on the circuit board contacts are shaped in the form of asphere and the probes are fabricated from a slender, elastic material.

The spherical contact assures that regardless of the angle of deflectionof the probe, as for example, in the case of the customary circuit boardcontacts consisting of metallized bores, there will be assured aconstant and complete annular bearing surface between the probe spherethe bore periphery and hence the equal contact pressure with acorresponding constant contact resistance. Moreover, because of the useof an elastic flexible material, the contact needle probes may movelaterally to compensate for and accommodate variations in the spacing ofthe contact grid field.

Vertical movement is also facilitated. Thus, the individual contactneedle probes are guided easily and slidably into electrically insulatedbearing bushings so that no variation or falsification of the contactforce occurs as a result of wall friction losses. Polytetrafluorethyleneis an example of a material that has been successfully employed in themanufacture of these bearing bushings. Advantageously the bearingbushings are constructed in the form of a collar to obtain long leakingpaths between the closely spaced individual probes.

According to an advantageous further development of our invention thecontact probes are covered with an insulated sleeving whereby thecontact probes coated with the insulated sleevings may slide directlyinto bores of a probe carrier. Thus, the distances between theindividual probes and the size of the bore in the needle probe carriermay be reduced so that maximum variations and sizes of the circuitboards may be tested by the apparatus. In addition, the mounting,changing and replacement of the probes is facilitated in that the probesand their connecting wires may be connected with one another prior toassemblage in the probe carriers. This preconnection rules out anybending of the probes or the danger of damaging already existingconnections.

It is also within the contemplation of this invention to eliminate theinfluence of atmospheric humidity on the contact resistances by heatingthe contact probes by means of resistance heaters built into the probecarriers.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantagesof the invention will be readily apparent from the following descriptionof certain preferred embodiments thereof, taken in conjunction with theaccompanying drawings, although variations and modifications may beeffected without departing from the spirit and scope of the novelconcepts of the disclosure and in which:

FIG. 1 is an elevational view partly in cross-section of a probe carrierand four probes according to a first embodiment of the invention;

FIG. 2 is a view looking up at the underside of a probe carrier and acarrier supporting means;

FIG. 3 is an enlarged blow up of three probes made according to thepresent invention illustrating their flexibility and engagement with thethree bore type contacts being tested;

FIG. 4 is an elevational side view in cross-section of a probe carrierand a probe according to a second embodiment of the invention;

FIG. Sis an elevational side view in cross-section of a probe carrierand a probe according to a third embodiment of the invention;

FIGS. 6 and 7 are elevational cross-sectional views of yet furtherembodiments of the probe contact head construction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. I there isshown an embodiment of the invention wherein a probe carrier generallyindicated at 17 includes a pair of spaced plates 18, 19 each havingcoaxial holes 18a, 19a therethrough. As shown for purposes ofillustration, four bushings, generally indicated at 10, 11, 12 and 13extend respectively through the holes 18a, 19a. Each bushing has anenlarged central portion 10a, 11a, 12a, and 13a respectively which,together with the member 1711 acts as a spacer for the carrier members18 and I9. Advantageously each of the bushings 10, ll, 12, and 13 may bemade of a polytetrafluorethylene so that probes generally indicated at20, 21, 22 and 23 may be guided easily and slidably therein. Thebushings 10, ll, 12 and 13 include collar-shaped portions 10b, 11b, 12band 13b respectively to produce long leaking paths between theindividual probes.

The probes 20, 21, 22 and 23 according to the present invention are madeof an elastic material such as spring steel for example, to enable theprobes to flex laterally and thereby accommodate any variations in thespacings of the bore type contacts of the grid field. At the end of eachof the probes 20 through 23 there are disposed contact spheres 30, 31,32 and 33 respectively which serve to engage the contacts to be tested.Of course, the probes and their respective spheres are of an electricconducting material and are conveniently attached adjacent their upperends to wires not shown. Vertical excellent movement of the probes isfacilitated by the relatively frictionless bushing material and by theprovision of coiled springs 40, 41, 42 and 43 respectively which, asshown, may surround their respective probes and bear between an enlargedcontact sphere and the lower surface of each probe bushing. Thefrictionless movement of the probes through 23 is increased by theprovision of an enlarged portion 100, 11c, 12c and 13c respectively sothat the probes are in contact with the bushings only at the oppositeends of the respective bushings.

One or more resistance heaters schematically illustrated at 60 may bedisposed in the probe carrier to heat the probes and thereby eliminatethe influence of atmospheric humidity on the contact resistances.

The relationship of the carrier 17 to a carrier support member 90 isshown in FIG. 2 in a view looking up at the underside of the probecarrier. Groups of probes generally indicated at 91 and 92 areschematically illustrated to show their relationship to the probecarrier. From this vantage point only the probe contact heads would bevisible. It will be understood that the number, size and arrangement ofthe probes will depend upon the particular circuit board being tested.From FIG. 2 it may be seen that the spacing of the probes and theiraccompanying contact heads may be very close thereby emphasizing theimportance of the slenderness of the probes and the advantages of theirflexibility.

The flexibility of the probes is further illustrated in FIG. 3 wherein aportion of the probes 20, 21 and 22 of FIG. 1 are shown as they mightappear in contact with boretype contacts 50, 51 and 52 respectively on acircuit board 53. The distances between the contacts of a printedcircuit board are exaggerated to illustrate the ability of the probes ofthe present invention to accommodate variations in the spacing distancesfrom predetermined rated values as a result of manufacturing conditions.The ability of the spherical contact heads 30, 31 and 32 to be fullyseated about the periphery of the openings 50a, 51a and 52a of the borecontacts 50, 51 and 52 respectively, regardless of the inclination ofthe probes 20, 21 and 22, may be clearly seen. As before, the biasingmeans 40, 41 and 42 act on the sphere to produce equal contact pressurewith its corresponding constant contact resistance. The probes 20,21 and22, being slidably held in the guide bushings 10, 11 and 12, are in aposition to adjust to the distances of the contacts 50, 51 and 52because of their elastic properties. The spherical shape of the probecontact heads 30, 31 and 32 allows them to lie in the metallized borecontacts thereby assuring constant and complete annular bearing surfacebetween the probe sphere and the bore.

In the embodiment of FIG. 4 there is shown an individual probe coveredwith a layer 81 of high quality insulating material which mayadvantageously be polytetrafluorethylene which has excellent slidingcharacteristics. In practice we have found it advantageous to providethe insulating material in the form of a tube that is slipped over theprobe. Because of the relatively frictionless characteristics of thepolytetrafluorethylene the bearing bushing such as shown at 10 forexample in FIG. 1 may be dispensed with. Again, however, to obtainsufficiently large leaking paths a spacer 48 made of a similar highquality insulating material is mounted between a soldering sleeve 64 anda probe carrier generally indicated at 27. For the same reason, a spacer67 is mounted between a contact head 35 and the coil spring 45. Theconnection of the probe with a wire means 83 is shown. A solderingcollar 64 attached to the upper end of the probe 25 provides a limit tothe downward movement of the probe. As set forth above the verticalmovement of the probe 25 through the close fitting holes 65, 66 in thecarrier 27 is made possible by the sliding qualities of the probecoating 81. As before, the probe 25 is also of slender construction andflexible laterally.

Since the printed circuit boards to be tested and for which the probesmust be arranged, may not all have the same contact bore diameters, andsince the ratio of the contact head diameter to the contact borediameter is predetennined, the probes such as 25 in FIG. 4 must beprovided with various sized contact heads depending upon the particularsize and arrangement of the printed circuit board being tested. To allowthe rapid change of the probe contact heads, a detachable one piececontact head 35 has been found advantageous. The head 35 may bedetachably connected to the probe 25 in any convenient manner. Thesemi-spherical head has been found very adequate.

In another embodiment the contact head may be of two parts as shown at37 in FIG. 6. Thus, the head 37 may be seen to comprise a tubular length37a having a sphere 37b welded thereon. 1n the two-piece type contacthead the diameter of the head 37b may be varied at will witheconomically justifiable means even when very small tests quantities areinvolved. There may be also used, as shown in FIG. 5, a thin-wallelastic metal tube 75 for the probe 26 which is likewise coated with alayer of high grade insulating material 82.

When the metal tube 75 is used as shown in FIG. 5, the provision of asoldered joint 76 between a lead 77 of a wire 84 and the probe 26 isexpedited since the copper conductor lead 77 may be directly insertedinto the bore of the tube 75 and thus consistently and perfectly fixedeach time. The soldered joint 76 itself may likewise be effected bymeans of a soldering sleeve not shown but as will be understood by thoseskilled in the art.

In the embodiment set forth in FIG. 5 the preconnected probe 26 withoutits contact head 36 or its insulating collar 68 is inserted directlyinto coaxial bores 85, 86 in the probe carrier member 47. Slidability ofthe probe 26 in the openings 85, 86 is facilitated by the slipperinessof the coating 82 on the probe 26. With the probe thus in place aresilient means such as a coil spring 46 may be slipped over the outsideofthe probe and held in position abutting the probe carrier 47 by acollar 68. The collar 68 in turn may be held in place by the contacthead 36. Various contact head constructions may be utilized such as thecontact rivet head shown at 36 in FIG. 5. In this case a pin portion 36aof the contact rivet 36 has an inside dimension corresponding to theinside dimensions of the tube 75. Attachment of the contact head 36 tothe probe 26 may be by any conventional means.

A further species of the contact head useful in the present invention isshown in FIG. 7 in which case the rivet contact head 38 consists ofa pin38a with a ball or sphere 38b welded thereon. As set forth with respectto the contact head 36 the contact head 38 may be attached to the probe26 by inserting the pin portion 38a in the tube 75. The readydetachability of the various contact heads 30, 31, 32, 33, 35, 36, 37and 38 permits their ready interchange so that spheres of variousdiameters may be used in accordance with the requirements of variouscircuit board contact sizes and arrangements.

The embodiment of the invention as shown in FIGS. 5 and 6, wherein theinsulation of the contact probes 25 and 26 is effected by means ofinsulated sleeve members 81, 82 respectively, facilitates the mountingof the probes in the probe carriers 27, 47 in compact, closely spacedrelationship thereby allowing easy accommodation of the wiring panels asis more clearly illustrated in FIG. 2 for example.

Operation of the testing apparatus may be understood in connection withFIGS. 2 and 3. Thus, with the probes such as herein illustrated at 20,21, 22, 23, 25 and 26 disposed in a group size shown at 91 and 92, whichgroups correspond in number and arrangement to the contacts on aparticular batch of circuit boards to be tested, a circuit board asillustrated at 53 having bore-type contacts 50, 51, and 52, is movedinto place below the probes. With the probes arranged to correspond tothe predetermined layout of the circuit board contacts most probes willassume the position as shown by the probe 22 in FIG. 3 whereby thespherical contact head 32 will be in contact with the upper peripheraledge 52a of the circular bore 52. The resilient member 42 biasing theprobe 22 downwardly will assure uniform contact pressure and henceuniform, low contact resistances which will provide accurate testing.If, because of variations within the manufacturing tolerances a circuitboard contact such as shown at 50 or 51 should be in a positiondifferent from the optimum position at which the probes were arranged,the spherical contact heads 30,31 will find their way into theirregularly spaced" boretype contacts because of, for example, theflexibility allowed by the probes 20, 21 because of the low frictionpoint contact between the spherical heads 30,31 and the surface of thecircuit board 53, and because of the downward biasing force of theresilient members 40, 41. Moreover, the probes will be perfectly seatedin the contacts with a constant and complete annular bearing surfacebetween the contact sphere and the contact bore periphery and henceprovide a constant contact resistance which will allow accurate andprecise testing regardless of the angle of the probe with the bore.

Although we have herein set forth our invention with respect to certainspecific principles and details thereof, it will be understood thatthese may be varied without departing from the spirit and scope of theinvention as set forth in the hereunto appended claims.

What we claim is:

1. An electrical testing apparatus for the simultaneous testing of aplurality of bore-type contacts of a circuit board comprising a carriermeans supporting a plurality of elongated, slender probe members, saidprobe members each having at a first end thereof a generally sphericallyshaped contact head enlarged with respect to said probe member, saidcontact head being adapted to be seated in one of said bore-typecontacts so that excellent electrical contact is effected therebetween,said contacts on said circuit boards being positioned thereon in apredetermined arrangement and said probes being positioned in saidcarrier means in a corresponding arrangement so that said sphericalcontact heads will each seat in a predetermined contact, said probesbeing flexible and axially slidably movable in said carrier so thatminor deviations in arrangement of said contacts may be accommodated bysaid probes, said individual probes having a resilient coil spring meansdisposed about said probe member between said probe carrier and saidcontact head.

2. A probe construction according to claim 1 wherein said probe membersare slidably guided through electrically insulated bearing bushings insaid carrier, said bushings being of a polytetrafluorethylene material.

3. A probe construction according to claim 1 wherein said probe membersinclude insulated sleeves forming the outer surface thereof, saidinsulated sleeves sliding directly in bores in said carrier means.

4. A probe construction according to claim 1 wherein said contact pointsare heated by means of resistant heaters disposed adjacent the probecarrier.

5. A probe construction according to claim 3 wherein said coil spring isdisposed about said insulated sleeve and in electrical connection withsaid contact head.

6. A probe construction according to claim 1 wherein said probe membersconsist of thin metal tubes.

7. A probe construction according to claim 2 wherein said bearingbushings take the form of a collar so that long leaking paths areprovided.

8. A probe construction according to claim 1 wherein said contact headsare detachably connected to said probe members.

9. A probe construction according to claim 8 wherein said contact headis a ball having a sleeve affixed thereto, said sleeve having an innerdiameter receiving the probe in a detachable frictional engagement.

10. A probe construction according to claim 8 wherein said contact headcomprises at least a semi-spherical portion having a pin means affixedthereto, said pin means being adapted to be received within a lower endof said probe member in gene rally axial alignment therewith.

1. An electrical testing apparatus for the simultaneous testing of aplurality of bore-type contacts of a circuit board comprising a carriermeans supporting a plurality of elongated, slender probe members, saidprobe members each having at a first end thereof a generally sphericallyshaped contact head enlarged with respect to said probe member, saidcontact head being adapted to be seated in one of said bore-typecontacts so that excellent electrical contact is effected therebetween,said contacts on said circuit boards being positioned thereon in apredetermined arrangement and said probes being posiTioned in saidcarrier means in a corresponding arrangement so that said sphericalcontact heads will each seat in a predetermined contact, said probesbeing flexible and axially slidably movable in said carrier so thatminor deviations in arrangement of said contacts may be accommodated bysaid probes, said individual probes having a resilient coil spring meansdisposed about said probe member between said probe carrier and saidcontact head.
 2. A probe construction according to claim 1 wherein saidprobe members are slidably guided through electrically insulated bearingbushings in said carrier, said bushings being of apolytetrafluorethylene material.
 3. A probe construction according toclaim 1 wherein said probe members include insulated sleeves forming theouter surface thereof, said insulated sleeves sliding directly in boresin said carrier means.
 4. A probe construction according to claim 1wherein said contact points are heated by means of resistant heatersdisposed adjacent the probe carrier.
 5. A probe construction accordingto claim 3 wherein said coil spring is disposed about said insulatedsleeve and in electrical connection with said contact head.
 6. A probeconstruction according to claim 1 wherein said probe members consist ofthin metal tubes.
 7. A probe construction according to claim 2 whereinsaid bearing bushings take the form of a collar so that long leakingpaths are provided.
 8. A probe construction according to claim 1 whereinsaid contact heads are detachably connected to said probe members.
 9. Aprobe construction according to claim 8 wherein said contact head is aball having a sleeve affixed thereto, said sleeve having an innerdiameter receiving the probe in a detachable frictional engagement. 10.A probe construction according to claim 8 wherein said contact headcomprises at least a semi-spherical portion having a pin means affixedthereto, said pin means being adapted to be received within a lower endof said probe member in generally axial alignment therewith.